1. Field of the Invention
The present invention relates to a method for locating mobile terminals, and more particularly to a method for locating mobile terminals located in an area where GPS assistance information required for location determination is not provided.
2. Description of the Related Art
As mobile terminals have become smaller, lighter, and more simple to use and mobile communication devices and their networks have spread worldwide, users of mobile communication services carry their mobile terminals and receive mobile communication services in addition to other services through their mobile terminals even when they travel. In the environment of a global system for mobile communications, many users also desire to receive application services (e.g., information on traffic, daily life, news, weather, location, etc.) using location information of their mobile terminals. A system to allow users to obtain their location information using the mobile terminals has been commercialized in some countries, for example, Korean mobile communication areas provided by SK telecom, KTF and the like, or Japanese or Western mobile communication areas of NTT, DoCoMo, Sprint PCS, KDDI, Vodafone and the like.
FIG. 1 is a schematic diagram showing the configuration of a general mobile communication system (particularly, a Global System for Mobile communication (GSM) or a Universal Mobile Telecommunication System (UMTS)). As shown in this figure, the GSM or UMTS includes a Core Network (CN) 110, a plurality of Radio Network Subsystems (RNSs) 120 and 130, and User Equipment (UE) 150.
The CN 110 manages information of UEs 150, and performs mobility management, session management and call management functions.
The RNS 120 or 130, serves to transfer data received from the CN 110 to users via an air interface. To this end, the RNS 120 or 130, includes a Radio Network Controller (RNC), and a plurality of base stations (node B). For example, the RNS 120 includes an RNC 121 and base stations (node B) 123 and 125, and the RNS 130 includes an RNC 131 and base stations (node B) 133 and 135.
RNC 121 or 131 is classified into a serving RNC (SRNC), a drift RNC (DRNC) and a controlling RNC (CRNC) based on its operation. The SRNC is an RNC that manages information of UEs belonging to the RNC, and handles data transmission between the UEs and the CN 110 via an Iu interface. The DRNC is an RNC that intermediates data transmission between a UE belonging to a different RNC and an RNC (for example, an SRNC) to which the UE belongs. The CRNC is an RNC that controls each of the base stations. For example, in FIG. 1, if the RNC 121 manages the information of the UE 150, the RNC 121 is an SRNC of the UE 150, and if the UE 150 moves and communicates data with the RNC 121 via the RNC 131, the RNC 131 is a DRNC of the UE 150. In addition, the RNC 121, which controls the base station (node B) 125 in communication with the UE 150, is a CRNC of the base station 125. In the example of FIG. 1, information and data of the UE 150 is transmitted and received to and from the CN 110 via the RNC 121 that is an SRNC of the UE 150.
There are various methods which are typically used for locating UEs in the mobile communication network. These methods are generally divided into three types which will be described below.
The first is a cell-based location method in which the location of a UE is determined based on information of a cell located nearest to the UE or based on information of a cell that manages the UE. The second is a network-based location method in which a signal measured between the node B and a UE is used to calculate a Time of Arrival (TOA) or a Time Difference of Arrival (TDOA) based on the intensity of the signal or based on radio wave transfer time thereof and the location of the UE is determined by triangulation using the calculated TOA or TDOA. The third is a GPS-based location method in which the location of a UE is determined using a Global Positioning System (GPS) developed by the US Department of Defense. One particular GPS-based location method, which complements and applies the GPS technology to a mobile communication network, is called Network-Assisted GPS (AGPS).
In the prior art, if a Location Service (LCS) client located external to a network requests location determination of a UE, a preparatory process for locating the UE is first performed, and a signal required to locate the UE is measured, and then the location of the UE is calculated based on the measured signal. In the preparatory process, a privacy indicator for limiting access to personal information or the like of the UE is read, and network resources are allocated, and then a location technique is selected according to the performance of the UE and the network, and quality of Service (QoS) requested by the LCS client. The location measurement process is performed between the Universal Terrestrial Random Access Network (UTRAN) and the UE. In this process, a location measurement signal, including a signal required to measure the location of the UE, is obtained and then the location of the UE is calculated using the location technique selected in the preparatory process. Here, the UE must be an individual UE whose Mobile Subscriber ISDN Number (MSISDN) or International Mobile Subscriber Identity (IMSI) is already known.
The above location measurement process is performed frequently when the UE moves out of a Gateway Mobile Location Center (GMLC), which is registered as a home GMLC of the UE in the CN, and it is thus located in another GMLC or when a location service for locating the UE is requested by an external LCS client or the UE itself. Here, the GMLC manages location information of UEs located in a Public Land Mobile Network (PLMN). The PLMN is a geographically or logically distinguishable mobile communication network, and one PLMN may include one or more GMLCs.
FIG. 2 is a process flow diagram showing a conventional method for locating mobile terminals, particularly when an external LCS client (hereinafter referred to as a “client”) 160 requests location determination of a UE_A 155.
As shown in FIG. 2, the client 160 requests a location service (LCS) of a UE, the location of which the client 160 desires to know, from a requesting GMLC 111 connected to the client 160 (S11). That is, the client 160 requests location information of the UE_A 155 from the requesting GMLC 111. The “requesting” GMLC 111 is a GMLC that “requests” location of the UE_A 155.
Then, the requesting GMLC 111 requests home PLMN information of the UE_A 155 from a Home Location Register/Home Subscriber Server (HLR/HSS) 115 (S13), and receives the home PLMN information from the HLR/HSS 115 (S15). As a server storing roaming information and registrant information of UEs, the HLR/HSS 115 responds to the request from the requesting GMLC 111 using the stored registrant information of the UEs. That is, in response to the request from the requesting GMLC 111, the HLR/HSS 115 provides the home PLMN information of the UE_A 155 to the requesting GMLC 111 (S15).
Then, using the home PLMN information of the UE_A 155 received from the HLR/HSS 115 at step S15, the requesting GMLC 111 requests information of a visited PLMN, where the UE_A 155 is currently located, from a home GMLC 113 of the UE_A 155 (S17). In response to the request from the requesting GMLC 111, the home GMLC 113 requests and receives information of the visited PLMN from the HLR/HSS 115 (S21, S23, respectively) after performing authentication for privacy protection (S19). Using the visited PLMN information, the home GMLC 113 requests the location information of the UE_A 155 from a GMLC 117 in the visited PLMN 20 (S25). Since it belongs to the visited PLMN where the UE_A 155 is currently located, the GMLC 117 is referred to as a “visited GMLC”.
The location of the UE_A 155 is calculated in the visited GMLC 117 in the PLMN being visited by the UE_A 155, an MSC/SGSN (Mobile-services Switching Center/Serving GPRS (General Packet Radio Service) Support Node) 119, a Radio Access Network (RAN) 170 and the UE_A 155 (S27).
As described above, the mobile communication network generally uses three location methods, i.e., a cell ID-based location method, a TDOA location method, and an A-GPS location method. The PLMN being visited by the UE_A 155 can also use one of the three location methods to measure the location of the UE_A 155. Depending on the burden on network resources or depending on where the location calculation is performed, the conventional location methods described above can be classified into the following two types. The first type is a UE-based location method in which the location of a UE is calculated by the UE itself based on pseudo range information and location assistance information. The second type is a UE-assisted location method in which a UE obtains pseudo range information using GPS assistance information (or A-GPS information) acquired from GPS satellite signals, and it then transfers the pseudo range information to an RNC managing an LCS service of the UE so that the location of the UE is calculated in the network.
In the example of FIG. 2, the request for the location information of the UE_A 155 transferred to the GMLC 117 being visited by the UE_A 155 is transferred to the RAN 170 via the MSC/SGSN 119. In the UE-based location method, a serving RNC of the UE_A 155 transmits its A-GPS information to the UE_A 155 so that the UE_A 155 calculates its own location. In the UE-assisted location method, the UE_A 155 transmits the acquired GPS pseudo range information to an RNC so that the location of the UE_A 155 is calculated in the network.
If the location of the UE_A 155 has been calculated based on one of the UE-based and UE-assisted methods at step S27, the visited GMLC 117 transfers the calculated location information of the UE_A 155 to the home GMLC 113. The home GMLC 113 transfers the location information received from the visited GMLC 117 to the client 160 via the requesting GMLC 111 (S33, S35) after again performing authentication (S31).
However, when an external LCS client or a UE requests a location service of the UE located in a PLMN that includes no location calculation system such as a Location Measurement Unit (LMU) or a Serving Mobile Location Center (SMLC), the conventional methods for locating mobile terminals (i.e., UEs) cannot calculate the location of the UE. That is, if the visited PLMN, where the UE is located, provides no location assistance information, the PLMN returns a failure response to the location measurement request from the UE or the LCS client.
The conventional location methods cannot obtain improved location service results over standalone GPS location measurement in a mobile communication network that provides no basic location service. For example, in the conventional location methods, an LCS client cannot obtain location information of a UE that is traveling to an accident area or is moving to a troubled area, and a UE cannot independently utilize travel or geographical information using an LCS service provided by its home PLMN, and also cannot independently check its location information to use an LCS service database stored in the UE.